The most important goals of every manufacturer are to meet customer required due dates and maintain high production yields. In semiconductor manufacturing, the production line usually operates 24 hours a day. Therefore, maintaining the production line balance and the production plan are the most troublesome tasks for planners and manufacturers.
There are many factors that influence the flow of work-in-progress (WIP) in a production line, including without limitation equipment resources, process judgments, WIP requirements, unexpected system failures. One of the more important of these factors is the supply and demand relationship between upstream/downstream production stages. In a WIP's process procedure (route), there are certain key production stages that require special treatments. These special treatments may involve, for example, special methods or longer than average processing time, which cause these stages to become production bottlenecks. The WIP flow often becomes abnormal when passing these key stages, if the production dispatching system cannot help to identify the abnormal situation. If the production line operators do not realize what is happening, the situation often becomes more serious. For example, if up-stream processing equipment fails and stops providing a certain kind of push WIP, and bottleneck processing equipment has been allocated to process the push WIP, the bottleneck equipment may incur a loss due to the lack of push WIP. This course of events creates a risk that the push WIP may miss its target, causing a waste of equipment utilization, and influencing the line balance.
In a production line, the production line operators typically obey the process instructions from leaders or supervisors. These process instructions are often derived from a production plan and a production target. However, since circumstances change virtually every second on the production line, the operators need a suggestion system to tell them what to do. One such suggestion system is a dispatch system. Conventional dispatch systems generate a dispatch WIP or lot list that records the number of WIPs or lots in the production line and the priority status of the WIPs. The dispatch WIP list enables the operators to realize how many WIPs are waiting for them and the urgency of each WIP.
Conventional dispatch WIP lists consider priority and other constrained conditions. Specifically, a conventional dispatch WIP list may contain explicit information such as processing technique, product identification (ID), queue time limit or future actions of the WIP, and implicit information such as the urgency level of the WIP and the necessity. Traditional dispatch WIP lists ignore the balance of demand and supply between upstream and downstream production stages. This is a problem because, in practice, an operator will typically check the first several lots on the dispatch WIP list even if there are 90 lots in the list, just to save reading time. If the first several lots are experimental lots, the operator may spend more time to find a production lot or just take the first lot. However, both of these actions wastes time, leads to line imbalance, and decreases the efficiency of production.
Accordingly, a method is needed for generating a dispatch WIP list that overcomes the deficiencies described above.